Crimped sleeve to tube pipe joints as presently known, are well known in the art, and because of significant advantages of the concept have gained acceptance for many uses.
Tube joints of this general type were first conceived of and described in U.S. Pat. No. 3,149,861 to Larson issued Sept. 22, 1964. As there described, a sleeve is compressively reduced, such as by crimping, onto a pipe end to provide the required interconnection between the sleeve and the pipe end.
There are many easy recognized advantages to the concept. Pipe joining can be accomplished without the need for welding or heat. Minimum pipe end preparation is required, and, the joint, once made, is permanent and not easily subject to tampering. However, in the practice of the technology many problems have arisen which have limited its application to small diameter pipes or tubes, and, as a result, its popularity has been restricted.
One significant impediment to more widespread adaptability is the limited resistance of such pipe joints to axial forces which occur upon pressurization of the pipeline incorporating the joint. Another problem is that the joint has little resistance to torsional loading.
Recognizing these problems, Mannesmann A. G. has over many years developed significant improvements in such joints. These have included modifications in the configuration of the crimped pattern as well as improved sealing means. These improvements have significantly enhanced the adaptability and market acceptance of crimped sleeve to tube pipe joints, sometimes referred to as the "press fitting system". As a result, its popularity has grown substantially.
Despite this, press fitting systems in current usage are limited to small diameter tubing, and, such systems are unable to satisfy the needs of users of relatively larger diameter tube. In those instances, the problems of inadequate axial and torsional resistance persisted.
In apparent recognition of these problems, it has been suggested in Japanese patent 88939 issued May 7, 1980 in the name of Nippon Benkan Kogyo K.K. that further modifications be made, particularly in the shape of the crimp. Other suggestions which would result in an increase in resistance to axial and torsional loading are made which incorporate a hexagonal crimp in the sleeve and the pipe, the hexagonal crimp being effective not only to resist axial separation of the sleeve and pipe, but also being effective to resist torsional loads that may be imposed on the joint. It is believed that the product described in the Japanese patent has not been marketed. Further, as hereinafter more fully set out in the Japanese patent, the configuration there described does not adequately solve the problem of providing sufficient resistance to separation of the sleeve from the tube.
When pressurized, internal pressure in the pipe acts to produce forces in an axial direction to cause separation of the sleeve from the pipe end. Pressure within the pipe also acts in radial directions to expand the crimped joint back to its in-round condition, which can result in release of the sleeve from the pipe end.
These conditions act in unison and if sufficient to cause a weakening of the joint the results can be quite serious, particularly if the pressurized fluid being conveyed is flammable, toxic, corrosive or acidic, or, is heated fluid, such as found in a domestic or industrial heating system.
As aforementioned, the formation of sleeve to tube joints generally involves the positioning of a sleeve over the pipe end. The sleeve includes a circumferential channel on its inner surface in which a sealing member, preferably an seal ring is received. The internal diameter of the sleeve and that of the seal ring must be sufficiently large to permit insertion of the sleeve and its contained seal ring onto the pipe end without cutting or abrading the seal ring, and, in the absence of an interference fit of the inner circumference of the sleeve with the exterior surface of the pipe.
As a result the inner circumferential length of the sleeve is greater than the outer circumferential length of the pipe. This inhibits continuous face to face seating of the sleeve onto the pipe during the crimping operation, unless some manner of shrinking the internal diameter of the sleeve can be devised. However, shrinking of the diameter of the sleeve poses unusual problems, in that the assembly of the joint will ordinarily take place at the actual site of the installation, and often times in locations that are not readily accessible and which require effecting the crimp in the joint from one lateral side of the joint.
Special crimping tools have been devised to accomplish this purpose, a suitable one being sold by Novopress GmBH & Co. KG. Thus, presently used crimping tools incorporate a pair of jaws that move towards the outer periphery of the sleeve, and effect the interconnecting crimp between the sleeve and the pipe. This movement of the jaws, however, results in displacement of the sleeve to an out of round condition relative to the pipe, and most importantly, results in uneven stressing of the seal ring. The body of the seal ring can move or displace circumferentially of the pipe from the location of first engagement of the crimping jaws to the position of terminal engagement of the crimping jaws.
This can result in uneven stressing of the seal ring, and is particularly disadvantageous where larger diameter sleeves and pipeline are to be used because it contributes to failure of the joint under pressure loading. Additionally, it severely limits the maximum internal pressure to which the piping system can be subjected without failure of the seal provided by the seal ring.
The present practice of employing a crimp having an hexagonal form simulating the exterior surfaces of a threaded nut does not overcome the problems. The pressure within the piping system acts radially outwardly on the flats of the hexagon, which have a low resistance to outward bowing, and, can cause outward ballooning of the flats, with a consequential decrease in the holding power of the joint, and subsequent failure of the joint.
The formation of a hexagonal crimp encircling the joint does have some advantage in that it increases resistance of the joint to torque loading. However, this is of only limited effect, in that the hexagonal crimped outer surface of the pipe has edges that can act as camming members operative to force the hexagonal crimp in the sleeve towards an in-round condition. If this should happen, the resistance of the joint to failure under pressure loading is seriously impaired.